I'll be finishing a basement, which has several yr old nice and flat concrete floor. The owner wants precautions taken to have it moisture-free when completed, and will be hiring a flooring contractor at some point. Concrete has dusty concrete residue (8 yr old construction.) when you swipe your finger.

Before doing the walls or anything, should the concrete floor be washed thoroughly and sealed?

The flooring has not been selected. It might be tile with/without radiant, or some sort of engineered wood, etc, so the final height could vary a bit. In this case, are jambs & doors typically installed after flooring is installed or beforehand?

Also, is there a list somewhere of things that must be in an install contract so whatever is selected is done properly? Such as "tile requires isolation membrane", flooring requires "X" glue, etc.)

Finally, if it were you, what flooring would you have in a basement bedroom? They would like it cozy, dry and quiet. They're thinking tile, but asked my advice. I think it's a rather "cold" solution. (This basement is has been dry and is expected to remain dry.)